Expression of heterologous genes in cells is desirable for many therapeutically relevant applications. One method of introducing a heterologous gene into a cell involves the use of transfer vectors which, when transfected into a host cell, induce the host cell to produce viral particles including the heterologous gene. The viral particles can then be used to infect a target cell, thereby inducing the target cell to express the heterologous gene. Viruses useful in such methods include lentiviruses, adenoviruses, and adeno-associated viruses. Some existing lentiviral vectors exhibit low gene expression levels and may be extremely large. In addition, there can be biosafety and toxicity concerns with respect to such vectors. As such, transfection and viral production using such vectors may be slow, inefficient, laborious, and expensive. Thus, a need exists for improved lentiviral vectors suitable for rapid and efficient production of viruses that are useful for inducing heterologous gene expression in target cells.